Top 20 most polluted cities: All but one in Asia

The majority of these cities – 13 – are in the world’s most populous country, India, where booming economic growth is fired largely by coal and where hundreds of millions live in traffic-clogged and congested megacities.

Another four are in neighboring Pakistan, with one in China and Kazakhstan respectively. CNN reported.

The only city outside of Asia featured on the list is N’Djamena, the capital of Chad in central Africa – which was named the country with the worst air pollution.

Meanwhile the cities with the worst pollution in North America were all in California.

The report by IQAir, a Swiss company that tracks global air quality, looked specifically at fine particulate matter, or PM2.5, one of the smallest but most dangerous pollutants.

PM2.5 comes from sources like the combustion of fossil fuels, dust storms and wildfires. It is so tiny – 1/20th of a width of a human hair – that it can travel past your body’s usual defenses into your lungs or bloodstream.

The particles cause irritation and inflammation and have been linked to respiratory problems and chronic kidney disease. Exposure can cause cancer, stroke or heart attacks and has been associated with a higher risk of depression and anxiety.

The World Health Organization (WHO) says average annual levels of PM2.5 should not exceed 5 micrograms per cubic meter.

Byrnihat, an industrial town in northeast India recorded a PM2.5 concentration of 128.2 last year – more than 25 times the WHO’s standard.

“It feels very sad and helpless that Byrnihat keeps topping the list ,” Suman Momin, 26, who lives in the city of around 70,000, told CNN.

She blamed factories around the town and a booming construction industry and trees being felled as contributing to the toxic air.